The present invention relates generally to the treatment and prevention of viral infections. In particular, the invention provides compositions and methods for the production of antibodies and peptides useful in the treatment and diagnosis of human immunodeficiency virus (HIV) infections.
The diagnosis, treatment and prevention of viral infections is a primary focus of many medical researchers. Although compositions and methods of diagnosing, treating and vaccinating against a number of viral infections are known, there are still a number of viruses which are difficult to detect in man and for which no effective methods of treatment or vaccination against are known. Of these, one of the most significant, of course, is HIV.
The infectious agent responsible for acquired immunodeficiency syndrome (AIDS) and its prodromal phases, AIDS-related complex (ARC) and lymphadenopathy syndrome (LAS), is a lymphotrophic retrovirus termed LAV, HTLV-III, ARV, and recently HIV as recommended by the International Committee on Taxonomy of Viruses (Ref 299). Nomenclature herein employs these recommendations to designated viruses associated with AIDS and the strains thereof. Historic references to strains, which include LAV and ARV-2, are now named HIV1 LAI and HIV1SF2, respectively.
As the spread of HIV reaches pandemic proportions, the treatment of infected individuals and prevention of the transmission to uninfected individuals at risk of exposure is of paramount concern. A variety of therapeutic strategies have targeted different stages in the life cycle of the virus and are outlined in Mitsuya and Broder, 1987, Nature 325:773. One approach involves the use of antibodies which bind to the virus and inhibit viral replication, either by interfering with viral entry into host cells or by some other mechanism. Once the viral component(s) susceptible to antibody intervention are identified, it has been hoped that antibody reactivity sufficient to neutralize the infectivity of the virus could be generated and administered to HIV-infected patients in the form of immune globulins or purified antibodies and that this passive immunization procedure would alter or reverse progression of HIV infection. In addition, it has been hoped that the vaccination of non-infected individuals with selected epitopes modified to enhance MHC interactions would provide protection from subsequent infection following exposure to HIV.
The envelope glycoproteins of most retroviruses are thought to react with receptor molecules on the surface of susceptible cells, thereby determining the virus"" infectivity for certain hosts. Antibodies that bind to these envelope glycoproteins may block the interaction of the virus with the cell receptors, neutralizing the infectivity of the virus. See generally, The Molecular Biology of Tumor Viruses, 534 (J. Tooze, ed., 1973); and RNA Tumor Viruses, 226, 236 (R. Weiss et al., eds., 1982); Gonzalez-Scarano et al., 1982, Virology 120:42 (La Crosse Virus); Matsuno and Inouye, 1983, Infect. Immun. 39:155 (Neonatal Calf Diarrhea Virus); and Mathews et al., 1982, J. Immunol., 129:2763 (Encephalomyelitis Virus). To date, therapeutic strategies directed at eliciting protective immune responses in man by vaccination with HIV proteins/peptides have failed. In addition, neither high titer neutralizing antibodies recovered from HIV-infected patients nor monoclonal antibodies produced in mice have succeeded in altering the progression of HIV infection to AIDS and death. There is a need in the art to identify alternate immunological targets on HIV which will elicit immune responses that will modify the course of HIV infection.
The general structure of HIV is that of a ribonucleo-protein core surrounded by a lipid-containing envelope which the virus acquires during the course of budding from the membrane of the infected host cell. Embedded within the envelope and projecting outward are the viral encoded alvcoproteins. The envelope glycoproteins of HIV are initially synthesized in the infected cell as a precursor molecule of 150,000-160,000 Daltons (gp 160), which is then processed in the cell into an N-terminal fragment of 110,000-120,000 Daltons (gp 120) to generate the external glycoprotein, and a C-terminal fragment of 41,000-46,000 Daltons (gp 41), which is the transmembrane envelope glycoprotein.
For the reasons discussed above, the gp 120 glycoprotein of HIV has been the object of much investigation as a potential target for interrupting the virus"" life cycle. Sera from HIV-infected individuals have been shown to neutralize HIV in vitro, and antibodies that bind to purified gp 120 are present in these sera, (Robert-Guroff et al., 1985, Nature 316:72; Weiss et al., 1985, Nature 316:69; and Mathews et al., 1986, Proc. Natl. Acad. Sci. U.S.A., 83:9709). Purified and recombinant gp 120 stimulated the production of neutralizing serum antibodies when used to immunize animals (Robey et al., 1986, Proc. Natl. Acad. Sci. U.S.A., 83:7023; Lasky et al., 1986, Science, 233:209) and a human (Zagury et al., 1986, Nature 326.249). Binding of the gp 120 molecule to the CD4 receptor also has been shown and monoclonal antibodies which recognize certain epitopes of the CD4 receptor have been shown to block HIV binding, syncytia formation, and infectivity. McDougal et al., (1986, Science 231:382) and Putney et al. (1986, Science 234:1392) elicited neutralizing serum antibodies in animals after immunizing with a recombinant fusion protein containing the carboxyl-terminal half of the gp 120 molecule and further demonstrated that glycosylation of the envelope protein is unnecessary for a neutralizing antibody response.
Shortly after HIV infection the immune system of man responds to the virus with both antibody production and cell mediated immune responses. A review of the immune responses to retroviruses has been published (Norley, S., and Kurth R., 1994: The Retroviridae, Vol E, J. A. Levy, ed., pp. 363-464, Plenum Press). Human antibodies specific for a number of HIV proteins including gp 160, gp 120, p66, p55, gp 41, p32, p24, and p17 have been reported (Carlson, 1988, J.Am. Med. Assoc. 206:674). The initial antibody response in man to HIV is directed to p17 and p24, followed by gp 120/160, then by gp 41, p66/55 and finally p32 (Lange J., et al 1986, Br. Med. J. 292:228). As HIV infection progresses into AIDS antibody levels to p17 and p24 markedly fall to undetectable limits and are replaced by p17 and p24 antigenemia. Antibody titers to p32 and p55 also decline but to a lesser degree (McDougal et al 1987 J. Clin. Invest. 80:316). However, substantial amounts of antibodies to gp 160/120 persist throughout the entire course of HIV infection. During the early phases of HIV infection an elevation in total immunoglobulins is observed and this increased quantity of antibody is specific for HIV and predominantly directed to gp 120, (Amadori et al., 1988 Clin. Immunol. Immunopathol. 46:342; Amadori et al, 1989, J. Immunol 143:2146). Possible mechanisms for this HIV specific hyper gamma globulinemia have been reviewed by Barker E. et al 1995: The Retroviridae Vol 4, J. A. Levy, ed. pp 1-96 Plenum Press. Functional properties and epitopes targeted by these antibodies produced during HIV infection have been described and include epitopes which are susceptible to antibody mediated neutralization. These primary target epitopes are primarily located on the envelope protein gp160 (gp120/gp41) and the gag protein p17; for review see Levy, 1994 Am.Soc. Micro; Nixon et al, 1992 Immunol 76:515. Neutralizing antibodies to HIV envelope protein have been identified and bind to conserved and divergent domains on gp 120. These include regions localized to the CD4 binding regions (Linsley et al 1988 and Thali et al, 1992); the second and third variable loop domains (Fung et al, 1992 and Haigwood et al 1990); and carbohydrate moieties (Benjouad et al, 1992 and Feizi and Larkin, 1990). Other neutralization sites have been identified on the external portion of gp 41 and a binding site on p17 (Changh et al, 1986). Early studies suggested that the presence of neutralizing antibodies lead to a more favorable clinical outcome, (Robert-Guroff et al, 1985). However, these studies employed selected sera with high neutralizing capacity against laboratory strains of HIV and not against autologous HIV isolates (Homsy et al, 1990; Tremblay and Wainberg, 1990). Subsequent investigation demonstrated that autologous antibody had little or no neutralizing activity against autologous HIV isolates (Homsy et al, 1990). The lack of susceptibility to antibody mediated neutralization in the presence of a neutralizing antibody is thought to result from the development of escape mutants that appear after seroconversion (Arendrup et al, 1992) and throughout the infection as new antibody specificities are produced. The clinical relevance of neutralizing antibodies produced as a consequence of HIV infection is unclear. However, it is clear that in spite of a vigorous immune response to HIV in individuals infected with HIV, progress to AIDS and, ultimately, death as a consequence of immune dysfunction predominates. Accordingly, new methods of treatment are sought.
It is an object of this invention to identify neutralizing regions of viral proteins which fail to elicit immune responses in man but do elicit immune responses in non-human mammals and to produce antibodies reactive with these regions. It is a further object of this invention to use these identified neutralizing regions of proteins and the antibodies reactive with them in the diagnosis, treatment and prevention of disease caused by the virus. Further objects of this invention will be apparent from the description of the invention detailed below.
In accordance with the present invention there are provided methods and compositions for the treatment, diagnosis and prevention of viral infection by the use of antibodies which react with regions of viral proteins to neutralize and inactivate functionally essential events in the life cycle of the virus. The antibodies recognize viral epitopes which fail to elicit an immune response in humans when encountered through infection or through environmental exposure but do elicit an immune response in non-human mammals.
Selected epitopes that react with nonhuman anti-viral antibodies but not with human anti-viral antibodies are identified. These epitopes escape surveillance by the human immune system through molecular mimicry to human proteins and in some instances are composed of amino acids susceptible to enzymatic cleavage in antigen processing cells. Desired epitopes are enzymatically cleaved by human enzymes and therefore are not processed for immune presentation.
Peptides representing these epitopes can be synthesized, optionally modified, and conjugated to a macrocarrier adjuvant to elicit antibody responses in non-humans. The preferred adjuvant is a microparticle comprising multiple repeats of muramyl dipeptide extracted from Propionibacterium acini. 
Antibodies and peptides of this invention can be used in immunoassay configurations to identify species specific epitopes and to quantitate viral antigens in human tissues and fluids. In a preferred embodiment, the invention provides antibody and peptide compositions and methods useful in the treatment and diagnosis of individuals infected with the virus.
In a preferred embodiment, the virus of interest is HIV.
The present invention provides novel compositions and methods for diagnosing and neutralizing viral infections. The invention will be described in detail with a focus on a preferred embodiment, in which the virus of interest is HIV. It is to be understood, however, that the principles of the invention can be used to identify neutralizing regions of proteins of other viruses and to produce antibodies reactive with those proteins that can be used to diagnose, treat and prevent infections caused by these other viruses as well.
Focusing now on HIV, this invention provides novel compositions and methods for neutralizing HIV infection and preventing or substantially inhibiting HIV infectivity, cell to cell transmission, and virus production in the infected host. More specifically, HIV protein sequences containing epitopes which fail to elicit an immune response in man when encountered through infection or naturally through the environment are utilized as described in detail below to produce antibodies in non-human mammals which can be administered to neutralize HIV infectivity, facilitate killing of infected CD4 lymphocytes, and inactivate essential steps in the life cycle of HIV. The term xe2x80x9cneutralizing regionxe2x80x9d indicates those portions of HIV, particularly HIV proteins, containing amino acid segments defining one or more epitopes reactive with antibodies which, either individually or in combination with other antibodies of the present invention, are capable of neutralizing HIV infections. Suitable assays for evaluating neutralization are well known and can include assays which measure reduction of HIV infections in T-cell lines, reduction of plaque forming units of VSV (HIV) pseudo types bearing the envelope glycoproteins of HIV, syncytial inhibition tests, and virion-receptor binding tests. The term xe2x80x9cinactivating regionxe2x80x9d indicates those segments of HIV proteins which contain one or more epitopes which when reacted with antibodies of this invention, either individually or in combination, inactivate functionally important events in the life cycle of HIV. Suitable assays to evaluate antibody-mediated destruction of HIV infected lymphocytes are well known and can include antibody dependent cell mediated cytotoxicity, complement mediated lysis, and natural killer (NK) assays. Suitable assays for measuring antibody-mediated inactivation of essential steps of the life cycle of HIV include assays which determine inactivation of reverse transcriptase, or measure polymerase and protease activity, or which evaluate antibody-mediated complement dependent changes in nuclear capsid permeability exposing viral RNA to ribonuclease degradation. As desired, the neutralizing activity can be compared to antibody reactivity in immunochemical assays, such as immunofluorescence, immunoblot, enzyme linked immuncassay, and radioimmunoassay.
The present invention is based on the discovery that epitopes which are functionally important in the life cycle of HIV, but not immunogenic in man, can be identified and characterized employing antibodies produced in selected mammalian species other than man. In addition, it has been discovered that the immunological non-responsiveness in man to these regions is a function of molecular mimicry and lack of MHC associated events, including antigen presentation through required MHC HLA class 1 and HLA class 2 associated events. With molecular mimicry the epitope is seen, as self and is not responded to under normal circumstances. With lack of MHC associated events in antigen presentation several steps are involved and failure of any one step can result in the absence of an immunological response to the antigen.
Peptide regions containing multiple overlapping epitopes and antibodies to these epitopes have been produced and are shown to neutralize and inactivate essential steps in the life cycle of HIV in vitro. In addition, HIV-infected patients with AIDS have been treated with antibodies to these peptide regions, resulting in rapid reduction in blood born infectivity measured by total culturable infectious dose (TCID). Treatment of chronic AIDS patients with these antibodies has resulted in marked clinical improvement, including weight gain, resolution of opportunistic infections, decreased incidence and severity of infections and doctor visits and resolution of HIV-associated neuropathy. The patients further have shown immunological recovery, as defined by a reduction of HIV-RNA, increased CD4 number, increased CD8 number and restoration of the cytokine system associated with improved CD4 and CD8 numbers and function.
Identification of Epitopes and Production of Antibodies
The majority of immune reactions target immunodominant epitopes. HIV epitopes are most frequently identified and mapped by various immunological methods which employ antisera to HIV, cytotoxic T lymphocyte reactivity to HIV epitope targets and helper lymphocyte antigen presentation of HIV epitopes. Synthetic peptides of known sequence which mimic HIV sequence can be employed competitively or noncompetitively using well known assays to confirm these observations. It is to be understood that stimulation of the immune system can lead either to enhancement or suppression of the immune response. Factors which govern this include:
A. The sub population of lymphocytes stimulated by the immunogen (Suppressor versus Helper.
B. The micro-environment, including cell population residing therein, which contact the immunogen first.
C. The type of cytokines present in the micro-environment at the time of effector cell contact with the immunogen.
D. The type of cytokines elicited following effector cell contact with the immunogen.
E. Structural and biochemical composition of the immunogen.
F. The amino acid sequence of the immunogen and its susceptibility to protease degradation by proteases in the micro environment.
From preliminary experiments, the following properties were determined to be fundamentally important in determining the potential value of certain proteins and peptides for use in the production of antibodies which are intended for passive immunotherapy application in the treatment or palliation of disease processes in man and, in particular, infection with HIV at all stages including AIDS:
A. The immunogen must lack epitope determinants that are expressed on human cells and tissues when employed to produce antibody for use in passive immunotherapy with the following exceptions:
1. Antigen distribution is restricted to sequestered and/or unavailable locations to the antibody.
2. The antigen is expressed during developmental phases which permit the use of antibody at specific times during the developmental cycle, when antigen is not available.
3. Epitope location within the host is not adjacent to a vital structure.
4. Antigen distribution on host cell is at a density lower than required to produce injury but favorable on the desired target resulting in selective targeting.
5. The target to normal ratio must be sufficiently different and favor antibody delivery to the desired target.
B. The number of peptide repeats delivered to an antigen-presenting cell directly influences the magnitude of the immunological response.
C. The epitope must not be present in body fluids at concentrations which would neutralize antibody and prevent targeting.
To date vaccine development has focused on designing better technology to amplify responses to targets to which the immune system of man responds, and passive immunotherapy has resulted in inconclusive results. Disclosed herein are alternate targets on HIV which do not elicit immune events in man as well as a new configuration to deliver antigen which results in immune reactions to HIV not previously attainable. The methods disclosed herein focus on the treatment of HIV and AIDS, but it is to be understood that the formulations of this invention have broad application. The antibody response in goats demonstrates utility of invention by way of antibody production to key targets on HIV, and by way of treatment which results in clinical improvement of AIDS. This technology has broad application in vaccine development.
Successful immune induction to antigen challenge requires the presentation of multiple epitope repeats by an antigen-presenting cell (APC) through MHC events. Epitopes which are most immunogenic are in an amphipathic configuration with a hydrophobic amino acid on one terminus, a hydrophilic amino acid on the other terminus, contain amino acids consistent with the formation of amphipathic helices; i.e., they lack helix breaking amino acids, such as proline, and lack carbohydrate. Sequences which lack amino acids that are susceptible to protease degradation by proteases in the micro-environment are especially desired.
To identify immunological targets on HIV with functional importance, immunogenic regions on HIV-related proteins in animal species other than man were determined. Goats were immunized with purified HIV lysate with and without carbohydrate groups removed. Removing carbohydrate residues from HIV proteins has little effect on the immunological response to the proteins yet can expose hidden epitopes. HIV lysates obtained commercially were further purified to remove proteins of tissue culture origins including human HLA class 1 antigens, HLA class 2 antigens, and beta-2-microglobulin. Following immunization, antisera from the goats were tested employing competitive immunoassay methodology to identify HIV peptides not recognized by antibodies pooled from HIV-infected patients. Pools of human HIV antisera were prepared from selected patient sera with high neutralizing and Western Blot activity and employed as competitive antibodies using standard competitive immunoassay methods. A broad spectrum of goat antibodies were identified which reacted with HIV determinants immunologically distinct from those recognized by the human anti-HIV antisera pools.
Those skilled in the art recognize that other animal species could be used to produce antibodies to these epitopes and that such antibodies could function in ADCC and complement mediated reactions. Other suitable animal species for the production of antibodies include, but are not limited to, sheep, rabbits, horses, cows and mice.
The epitope reactivity of the anti-HIV antibodies was characterized using twelve-mer peptides spanning the linear amino acid sequences of HIV1SF2. Peptides of this size react well with antibodies, can be synthesized easily and can be prepared in highly purified form. Peptides were synthesized by and purchased from Purification Systems, Inc. The synthetic peptides were combined with peroxidase labeled goat anti-HIV antibodies and combined with each of two sets of microtiter wells coated with HIV. One set was blocked with human IgG anti-HIV; the other set was not. The percent of peptide inhibition of goat anti-HIV binding to HIV protein sites blocked with human anti-HIV was determined.
When inhibition of binding was observed with a specific synthetic peptide, additional peptides were synthesized with amino acid sequences overlapping that of the original inhibiting peptide to further define the epitope sequences.
The location of the epitopes on the HIV proteins recognized by goat anti-HIV IgG but not human anti-HIV IgG were further evaluated and confirmed using HIV peptide-HRP conjugates as the identification markers. In this assay, HIV proteins were absorbed to supports such as microtiter plate wells or precision polystyrene beads. Twelve-mer peptides spanning the linear amino acid sequence of HIV1SF2 were covalently attached to horseradish peroxidase. Human and goat anti-HIV reactivity were measured independently with anti-HIV reactivity from human and goat bridging the native epitopes adsorbed to the support and to the peptide epitope covalently attached to peroxidase. With this procedure, detailed in Example 8, only exact epitopes contained within the synthetic peptide were recognized.
Once peptides having significant mimicry with human proteins have been identified, those sequences which have functional importance in the life cycle of HIV are determined. This is done, as described below and illustrated in Example 8, by generating antibodies to candidate peptides and then testing those antibodies for their effects on HIV infectivity and viral neutralization.
As noted above, a number of specific epitope regions have been identified and nine are described in detail below with reference to the HIV1SF2 sequence unless otherwise indicated. Amino acid residue designations set forth below and throughout this application for HIV1SF2 are from the Los Alamos Data Bank (AIDS Virus Sequence Data Base, Los Alamos National Laboratories, Theoretical Division, Los Alamos, N.M. 87545). Amino acid residue designations set forth below and throughout this application for HIV2NZ are from the Ex Pasy World Wide Web Molecular Biology Server of the Geneva University Hospital and the University of Geneva, and the BioAccelerator available through Compugen Ltd. at the Weizman Institute, Israel, and Akira Ohyama, BioScience Systems Department, Mitsuey Knowledge Industry Co., Ltd., Tokyo, Japan. Those skilled in the art will appreciate that additional analogous regions (xe2x80x9chomologsxe2x80x9d) from other HIV isolates can be identified based upon their location within related proteins from various isolates. In practice, such homologs can be identified by reference to HIV1SF2 sequence data as follows:
(a) the amino acid sequences of HIV isolates and HIV1SF2 can be aligned to obtain maximum homology between the two sequences, generally at least about 75% identify between the sequences;
(b) once an amino acid sequence is aligned to the corresponding location within HIV1SF2 proteins will demonstrate immunological mimicry, similarity, or identity with HIV1SF2 as defined by retention of antibody reactivity to the mimicked or homologous sequence. Peptides from other HIV isolates and their amino acid sequences so identified typically will immunologically mimic corresponding regions on HIV1SF2.
This method of identifying key epitopes can be applied to HIV strains that are yet to be discovered. For example, as new strains of HIV are identified, their envelope and core amino acid sequences can be aligned with that of HIV1SF2 to obtain maximum sequence homology with that strain. The methods by which the sequences are aligned are known to those skilled in the art. In aligning the sequences it is desired to maintain as much homology between cysteine residues as possible. The amino acid sequence(s) of the new HIV strain or species which corresponds to the location of the peptides specifically disclosed herein can be synthesized and used in accordance with the invention.
It is not necessary to the present invention that the epitopes contained within such sequences be cross-reactive with antibodies to all strains or species of HIV. Peptides encompassing immunological epitopes which distinguish one species or serogroup over another will find utility in identifying particular species or serogroups and may assist in identifying individuals infected with one or more species or serogroups of HIV. They also can be useful in combination with other peptides, from either a homologous region or another neutralizing region, in therapeutic regimens.
The amino acid sequences of this invention typically comprise from about 5 to about 50 amino acids and comprise an epitope region or multiple epitope regions located on HIV proteins that fail to elicit a protective immune response in man when encountered through infection or environmental contact but do elicit a response in a non-human mammal. Preferably, the sequences comprise between about 5 and 35 amino acids. Synthetic peptides or treated lysates of natural HIV proteins containing the desired amino acid sequences are used to immunize animals which respond immunologically to them and produce antibodies which have therapeutic value in treating HIV infections.
The amino acid sequences or peptides of interest fail to elicit an immune response in man through mimicry of epitopes on human and other proteins. Of particular interest are peptide epitopes shared between HIV proteins and human alpha fetoprotein, aspartyl protease, deoxyuridine 5xe2x80x2-triphosphate nucleotidohydrolase, eosinophil cationic protein, eosinophil-derived neurotoxin and ribonuclease 4 precursor and peptide epitope regions mimicked by neurotoxins from Bungaris Naja, Dendoaspis, Psudechis, or Androctonus Centruroides.
In the discussion which follows, reference is made to a number of human proteins and neurotoxins using standard identifying abbreviations for the proteins. Set forth below is a table which sets forth these abbreviations and the full names of the proteins to which they correspond:
The amino acid sequences of nine of the highly conserved epitope regions discussed above are provided below. Three of these regions are on the envelope glycoproteins gp120 (two targets) and gp41 (one target), one is on the reverse transcriptase heterodimer p66/55, and one is on protease p10. Additional targets are on the Gag precursor (p55/Gag) with sites on p17 (two targets), p24 and p7.
One epitope region on HIV1SF2 gp120 extends from amino acid residue 4 through 27 and a second extends from amino acid residue 54 through 76 of HIV1. Antibodies to epitope regions located on gp120 function synergistically to effect the release of gp120 from gp41. The release of gp120 from gp41 is antibody dose dependent and can be demonstrated by neutralization assays, such as TCID, which measure HIV infectivity.
An epitope region of a neutralizing or inactivating region of gp120 of HIV2NZ also has been determined. The sequence of HIV2 envelope glycoprotein gp120 has been mapped, and from about amino acid residue 7 through 43 is a region mimicking a sequence of HIV1SF2 gp120 and certain human proteins. Antibody targeting the region results in dissociation of HIV2 gp120 from gp41, which correlates with a reduction in infectivity.
A third HIV envelope glycoprotein target for HIV1SF2 was located at amino acid residues 502-541 of gp41 transmembrane glycoprotein. Antibody targeting of this region in the presence of complement results in an antibody dependent complement mediated lysis of the HIV envelope glycoprotein and marked reduction in HIV infectivity.
In addition to the envelope glycoprotein epitope regions, another HIV1 epitope region of interest includes amino acid residues 254 through 295 of the reverse transcriptase heterodimer p66/55. Antibody targeting of this region results in an antibody dose dependent reduction in reverse transcriptase activity. Also of interest is the epitope region encompassing amino acid residues 69-94 of protease p10. Antibody targeting of this region results in an antibody dose dependent reduction in protease activity.
The targets on reverse transcriptase and protease are in conserved regions adjacent to the enzyme active site, which is well-known for its mutation and subsequent resistance to competitive inhibitors. The antibody-mediated inactivation results from a steric or conformational change in the enzyme with secondary loss of activity. This method of inactivation functions independently and is not influenced by mutation in the enzyme active site and is irreversible.
Also of interest are three epitope regions within the Gag gene. Specifically, amino acid residues 166 through 181 of Gag gene protein p24, one target at amino acid residues 2 through 23 and a second target at amino acid residues 89 through 122 of Gag gene protein p17 and amino acid residues 390 through 410 and 438 through 443 of Gag gene protein p7 are useful in this invention. Antibodies targeting these regions result in disruption of the nuclear capsid following lysis of the HIV envelope by the antibodies described above. This targeting culminates with exposure of HIV RNA to plasma RNAse degradation. Additionally, the targets on p17 is exposed on the surface of infected lymphocytes following budding. This provides an additional target for ADCC lysis of infected lymphocytes.
One of the specific peptides set forth above, comprising at least one epitope not recognized by antibodies from HIV-infected patients but recognized by goat anti-HIV antibodies, is the peptide comprising amino acid residues 4 through 27 of HIV1SF2 envelope gp120 protein and linear epitope-containing subsequences thereof, which has the following sequence:
This peptide mimics human proteins FOL1, NTCR, PIP5, PSS1, KITK, MC5R, ECP, INIU, INI9, VPRT, CD69, MYSE, RNKD, ACHE, TCO2, LCAT, MAG1, MAG2, MAG3 and LYOX.
A second epitope region from the HIV1SF2 gp120 envelope glycoprotein extends from amino acid residue 54 through 76, which has the sequence:
This peptide mimics proteins CYRB and SYV.
A third epitope region of interest in the envelope of HIV1SF2 extends from amino acid residue numbers 502 through 541 of glycoprotein gp41. This peptide has the following amino acid sequence:
This peptide mimics human proteins CYPC, TYK2, ACHE, NTCF, NTCR, CD81, 41BL, NIDO, GSHR, CO02 and TCO2.
In another specific embodiment, an epitope region of interest is that of amino acid residues 2 through 23 of the HIV1SF2 Gag protein p17. This peptide has the sequence:
This peptide mimics human proteins TFPI, PA2M, BLSA, ECP, and FETA and certain neurotoxins, such as NXS1 and NAJAT. The peptide has a hydrophobic sequence which binds to and targets host cell membrane and function mimics cellular translation protein Src.
A second target on HIV1SF2 p17 extends from amino acid residue 89 through 122. This peptide has the sequence:
This peptide mimics FETA and TRIC.
Another peptide of interest is that of amino acid residues 166 through 181 of the Gag gene protein p24 and epitope containing subsequences therein. This peptide has the sequence:
This peptide mimics human proteins FETA and TRFL.
A third Gag gene protein epitope region of interest is the peptide having amino acid residues 390 through 410 and 438-443 of Gag gene protein p7 and epitope containing subsequences thereof. This peptide has the sequence:
This peptide mimics human FETA and RNA binding proteins. This peptide contains a zinc binding domain which interacts with, and binds to, viral RNA. Antibodies to this region enhance the removal of premature HIV devoid of envelope following the lysis of infected CD4+ lymphocytes.
Also of interest as an epitope region is the peptide of amino acid residues 69 through 94 of the protease p10 and epitope-containing subsequences thereof. This peptide has the sequence:
This peptide sequence mimics human proteins RENI, BLSA, VPRT and CATD. Antibodies to this sequence inhibit the protease activity of HIV.
A further specific sequence useful in this invention is a sequence encompassing amino acid residues 254 through 295 of HIV1 reverse transcriptase heterodimer p66/55. This peptide has the sequence:
This peptide sequence mimics human proteins POL1 and ECP.
As noted above, other strains of HIV also can be used to obtain peptides and antibodies in accordance with the present invention. Useful peptides from other strains can be determined by comparing and aligning the sequence of another strain to the sequence of HIV1SF2 or HIV2NZ and finding that part of the sequence homologous to the epitopes of interest identified for HIV1SF2 or HIV2NZ.
A sequence of interest in HIV2NZ identified by the method of this invention is in the env gp120 open reading frame and extends from amino acid residue numbers 7 through 43. This peptide has the following sequence:
This peptide mimics human proteins IL9, SRE1, NRM1, LBP, NOL1, S5A2, LMA1, LECH, LFA3, KPLC, FETA, 3BH2, 3BH1, INR2 and EV2B.
For example, once the desired amino acid sequences have been identified, antibodies which recognize these sequences are obtained. Such antibodies can be obtained using proteins containing the peptides isolated from HIV lysates, synthetic peptides, bacterial fusion proteins and proteins/peptides from phylogenetically unrelated sources which contain the desired epitopes.
If viral lysates are to be used, a protein lysate of a single HIV strain can be used, or a mixture of lysates of two or more different strains can be used. If a mixture of lysates is used, the mixture can comprise lysates of different HIV1 strains or a combination of at least one HIV1 strain and at least one HIV2 strain. A preferred mixture is a combination of lysates from HIV1BAL, HIV1MN and HIV2NZ.
Viral lysates initially are treated to remove lipids and other impurities from the HIV proteins. The HIV protein mixture then is treated to remove contaminants of cell culture origin, including human leukocyte antigen (HLA), class I and class II antigens. Methods for removing these antigens are known in the art and include employing monoclonal anti-HLA class I and anti-HLA class II antibodies and immunoaffinity procedures; one method is set forth in detail in Example 3 below.
In addition, it has been found that carbohydrates of the HIV proteins must be removed; phylogenically preserved carbohydrates determinants otherwise would stimulate immune responses when the HIV proteins are administered to an animal, resulting in the production of antibodies which would be cytotoxic against human tissues. The proteins are treated with enzymes known to those skilled in the art to remove carbohydrates, including PGNase, neuraminidase and glycosidase. One such method is described in detail in Example 3.
The mixture of treated HIV proteins then can be used to immunize an animal to produce antibodies to the peptides of interest. Desirably, the mixture contains approximately equal amounts of the proteins comprising the peptides or epitope regions of interest. That is, desirably they are provided in proportions of approximately 1:1 and the difference in molar ratios between any two peptides is no greater than about 10:1, preferably 3:1.
Alternatively, synthetic peptides can be used as the immunogen. If synthetic peptides are used the amino acid sequence of any desired peptide can be modified by, for example, using a substituted or truncated form of the amino acid sequence.
Amino acid substitutions can be made to avoid predicted enzymatic cleavage that can occur during antigen processing at a particular amino acid moiety, to force amphipathic conformation to meet required MHC-associated antigen presentation and to provide sufficient length for HLA presentation should cleavage occur at or near the epitope boundary. Truncated sequences are selected such that the peptide will retain conformity to epitope length requirements as predicted by MHC class 1 and class 2 antigen presentation motifs. More extensive guidelines on desirable amino acid substitutions are given below as part of the section on synthetic peptides. In addition to substituted and truncated sequences, extended sequences can be prepared in which additional amino acids are added at either end of a selected epitope region for the purpose of facilitating attachment to solid phase supports and macromolecular carriers.
As an example, useful truncated sequences of the peptide extending from amino acid residue 502 through 541 of HIV1SF2 gp41 discussed above include a peptide with the sequence of amino acid residues 512-531:
and also a sequence extending from amino acid residue 518 through amino acid residue 527:
Another particularly useful truncated peptide is a truncated sequence of the peptide extending from amino acid 7 through 43 of gp120 of HIV2NZ has the following sequence.
The peptide can be prepared in a wide variety of ways. The peptide, because of its relatively small size, can be synthesized in solution or on a solid support in accordance with conventional techniques. Various automatic synthesizers are commercially available today and can be used in accordance with known protocols. See, for example, Stewart and Young, Solid Phase Peptide Synthesis, 2nd ed., Pierce Chemical Co., 1984; and Tam et al., J. Am Chem. Soc. (1983) 105:6442.
Alternatively, hybrid DNA technology can be employed where a synthetic gene is prepared by employing single strands which code for the polypeptide or substantially complementary strands thereof, where the single strands overlap and can be brought together in an annealing medium so as to hybridize. The hybridized strands then can be ligated to form the complete gene, and, by choice of appropriate termini, the gene can be inserted into an expression vector, many of which are readily available today. See, for example, Maniatis et al., Molecular Cloning, A Laboratory Manual, CSH, Cold Spring Harbor Laboratory, 1982. Or, the region of the viral genome coding for the peptide can be cloned by conventional recombinant DNA techniques and expressed in procaryotic or eukaryotic expression systems to produce the desired peptides.
Preferably, the immunogen will be enriched for the desired epitopes to which antibody-producing B lymphocytes will respond by producing antibodies that will neutralize and inactivate essential steps in the life cycle of HIV infection. As used herein, xe2x80x9cenrichedxe2x80x9d means that a desired epitope constitutes at least 25% of the HIV protein, preferably at least 50%, and most preferably about 95%. More particularly, solutions containing disrupted virus lysate or extracts, or supernatant of biologically-expressed recombinant proteins or disrupted expression vectors or proteins containing mimicked epitopes can be enriched for such proteins, as desired, using purification methods, such as, for example, polyacrylamide gel electrophoresis. Immunoaffinity purification is a preferred and convenient method for purification of proteins and peptides containing the desired HIV epitopes, e.g., affinity purification using mono specific affinity purified polyclonal or monoclonal antibodies. The extent to which the peptides are purified from the solutions for use as an immunogen can vary widely, i.e., from about 50%, typically at least 75% to 95%, desirably 95% to 99% and, most desirably, to absolute homogeneity.
To obtain antibodies to the desired epitopes, animals are immunized with either the peptides of interest or HIV proteins containing them which have been treated to remove carbohydrates and HLA antigens as disclosed above. Immunization protocols are well known and can vary considerably yet remain effective. See Colco, Current Protocols in Immunology, John Wiley and Sons, Inc. 1995. The proteins and/or peptides can be suspended or diluted in an appropriate physiological carrier for immunization. Suitable carriers are any biologically compatible, non-toxic substance to deliver and/or enhance the immunogenicity of the peptides, including sterile water and 0.9% saline.
Alternatively, the peptides can be coupled to a carrier molecule before being used as an immunogen. One preferred technique, for example, discussed in more detail below, involves the attachment of the proteins and fragments thereof to multiple repeats of a glycopeptide, such as muramyl dipeptide (MDP), to form a microparticle, typically less than 1 micron, and preferably less than 0.2 microns, in diameter. The microparticle then can be dispersed in a pharmaceutical carrier for injection. This procedure achieves a high density of the peptide which can be used to elicit the desired immune response. The selection of carrier will vary depending upon the route of administration and response. The compositions can be sterilized by conventional, well-known sterilization techniques. The peptides can be administered by oral or parenteral routes, preferably the latter.
Immunogenic amounts of antigenic preparations enriched for the desired epitopes are injected, generally at concentrations in the range of 1 xcexcg to 20 mg/kg body weight of host. Administration can be by injection, e.g., intramuscularly, peritoneally, subcutaneously, intravenously, etc. Administration can be one time or a plurality of times, usually at one to four week intervals.
Immunized animals are monitored for production of antibody to the desired epitope. High affinity complement fixing IgG antibody is preferred for passive immunotherapy and can be used intact or as fragments such as Fv, Fab, F(abxe2x80x2)2. Antibody fragments may be preferable when greater tissue penetration is desirable. Antibodies and fragments can be given alone or as conjugates with toxic substances or isotopes. Once the desired antibody response is attained, blood is collected by, for example, venipuncture, cardiac puncture, or plasmapheresis. Antibodies are purified from the complex serum or plasma mixture in accordance with conventional procedures, including, for example, salt precipitation, ion exchange chromatography, size chromatography, affinity chromatography. Oftentimes, a combination of methods is used. Immunoaffinity chromatography is a preferred method.
To circumvent possible antigenicity in a human receiving antibody derived from a non-human animal, recombinant antibodies can be constructed. One type of recombinant antibody is a chimeric antibody, wherein the antigen binding fragment of an immunoglobulin molecule (variable region) is connected by a peptide linkage to at least part of another protein not recognized as foreign by humans, such as the constant portion of a human immunoglobulin molecule. This can be accomplished by fusing the animal variable region exons with human kappa or gamma constant region exons. Various techniques are known to the skilled artisan, such as those described in PCT 86/01533, EP171496, and EP173494, the disclosures of which are incorporated herein by reference. A preferred type of recombinant antibodies is CDR-grafted antibodies.
The antibodies of this invention that neutralize infectivity, kill infected CD4 lymphocytes and inactivate functionally important events in the life cycle of HIV are incorporated as components of pharmaceutical compositions. The compositions comprise a therapeutic or prophylactic amount of at least one of the antibodies of this invention, and desirably an antibody cocktail, with a pharmaceutically acceptable carrier. A pharmaceutically acceptable carrier is any compatible, non-toxic substance suitable for the delivery of the antibodies to the patient. Thus, this invention provides compositions for parenteral administration which comprise a solution of antibody dissolved in an acceptable carrier, preferably an aqueous carrier. A variety of aqueous carriers can be used, e.g., water, buffered water, 0.4% saline, 0.9% saline, 0.3% glycine and the like. These solutions are sterile and generally free of particulate matter. The compositions further can comprise pharmaceutically acceptable auxiliary substances as required to approximate physiological conditions, such as pH adjusting and buffering agents, toxicity adjusting agents and the like. For example, sodium acetate, sodium chloride, potassium chloride, calcium chloride, sodium lactate, etc., can be used. The concentration of antibody in these formulations can vary, typically from less than about 0.1 mg/ml to as much as 150 or 200 mg/ml, preferably between about 1 mg/ml and about 20 mg/ml, and will be selected primarily based on fluid volumes, viscosities, etc., preferably for the particular mode of administration selected. Determining the concentration of a particular antibody or antibody cocktail is within the abilities of one of ordinary skill in the art. Thus, a typical pharmaceutical composition for intravenous infusion can be made up to contain 250 ml of sterile Ringer""s solution and 100-200 mg of antibody. Compositions for intramuscular injection can be made up to contain 1 ml sterile buffered water and about 20 to about 50 mg of antibody. Actual methods for preparing parenterally administrable compositions will be known or apparent to those skilled in the art and are described in more detail in, for example, Remington""s Pharmaceutical Science, 15th Ed., Mack Publishing Company, Easton, Pa. (1980), which is incorporated herein by reference. Such compositions can contain a single antibody which is, for example, specific for certain strains of HIV or for a single protein or glycoprotein expressed by most and, more preferably, all strains of HIV. Alternatively, a pharmaceutical composition can contain more than one antibody to form a xe2x80x9ccocktail.xe2x80x9d For example, a cocktail containing antibodies against various proteins and strains of HIV would be a universal product with therapeutic or prophylactic activity against the great majority of the clinical isolates of HIV. The cocktail can contain antibodies which bind to epitopes on proteins or glycoproteins of the HIV envelope, for example, or can contain a combination of antibodies to epitope sites identified above on HIV1SF2 Env proteins gp160, gp120, and gp41; Gag protein p7, p17 and p24; reverse transcriptase heterodimer p66/55 and protease p10, or a subgroup thereof, thus neutralizing a series of epitopes crucial in the life cycle of HIV. Antibodies to epitope sites on other neutralizing or inactivating regions of HIV proteins also, of course, can be employed.
For example, antibodies which modify attachment, cell entry, transcription, translation, assembly, targeting of the mature virion to the plasma membrane and extrusion of the virion will interfere with HIV life cycle events. Antibody cocktails will more frequently be employed to obtain inactivation of multiple essential HIV proteins. This will be of therapeutic benefit in particular within virions lacking the outer envelope but possibly are infectious should they gain cell entry by other mechanisms such as micro-pinocytosis or transfection or the like. The molar ratio of the various antibody components usually will not differ by more than a factor of 10, more usually by not more than a factor of 5, and will usually be in a molar ratio of about 1:1-3 to each of the other antibody components.
With respect to antibodies to the nine specific peptides set forth above, a desirable antibody cocktail comprises antibodies to the two envelope gp120 peptides and gp41 peptide. More desirably, the cocktail comprises antibodies to those three epitope regions plus an antibody to the protease p10 epitope region. Even more desirably, the cocktail comprises antibodies to those four epitope regions plus antibodies to at least one of the other five enumerated epitope regions. In a most preferred embodiment, the cocktail comprises antibodies to all nine of the epitope regions.
The antibodies and antibody cocktails of the present invention can be administered independently or given in conjunction with other anti-retroviral agents. The current status of the development of other anti-retroviral agents, and of anti-HIV agents in particular, is reviewed in Mitsuya et al., Nature 325:773-778, 1987.
The antibodies and peptides of this invention can be stored in liquid format at various temperatures known to preserve antibody activity, e.g. xe2x88x9270xc2x0 C., xe2x88x9240xc2x0 C., xe2x88x9220xc2x0 C., and 0-4xc2x0 C. or lyophilized for storage and reconstituted in a suitable carrier prior to use. This technique has been shown to be effective with conventional immune globulins, purified antibodies, and immunogens composed of proteins, glycoproteins, and peptides. Art-known lyophilization and reconstitution techniques can be employed and it will be appreciated by those skilled in the art that lyophilization and reconstitution can lead to varying degrees of antibody activity loss (e.g., with conventional immune globulins, IgM antibodies tend to have greater activity loss than IgG antibodies) and that doses may have to be adjusted to compensate for any loss.
The compositions containing the present antibodies or cocktails thereof can be administered for the therapeutic and/or prophylactic treatment of HIV infections. In therapeutic application, compositions are administered to a patient already infected with HIV, in an amount sufficient to treat or at least partially arrest the infection and its complications. An amount adequate to accomplish this is defined as a xe2x80x9ctherapeutically effective dose.xe2x80x9d Amounts effective for this use will depend upon the severity of the infection and the general state of the patient""s own immune system, but generally range from about 0.1 to about 200 mg of antibody per kilogram of body weight with dosages of from 0.5 to 25 mg per kilogram being preferred. The compositions of this invention can be employed in serious disease states that are life-threatening or potentially life-threatening situations. In such cases, it is possible and may be felt desirable by the treating physician to administer substantial excesses of these antibodies.
In prophylactic applications, compositions containing the present antibodies or a cocktail thereof are administered to a patient not already infected by HIV, but perhaps recently exposed to or thought to have been exposed to, or at risk of being exposed to the virus (such as, for example, the newborn of an HIV infected individual), or immediately following an exposure or suspected exposure to HIV. If the composition is to be administered to an HIV-infected pregnant female, it can be given once or multiple times prior to delivery to reduce HIV infectivity in maternal blood and thereby reduce the risk of HIV transmission to the newborn. The newborn at risk also can be treated to further reduce the risk of contracting HIV. An amount defined to be a xe2x80x9cprophylactically effective dosexe2x80x9d generally ranges from 0.1 mg to 25 mg per kilogram of body weight, depending upon the patient""s state of health and general level of immunity.
In addition, the antibodies of the present invention can find use as a target-specific carrier molecule. An antibody can be bound to a toxin to form an immunotoxin or a radioactive material or drug to form a radiopharmaceutical or pharmaceutical. Methods for producing immunotoxins and radiopharmaceuticals are well known (see, for example, Cancer Treatment Reports 68:317 (1984)). Heteroaggregates of antibodies of the present invention and human T-cell activators, such as monoclonal antibodies to the CD3 antigen or to the Fc gamma receptor on T-cells, can enable human T-cells or Fc-gamma bearing cells (such as K cells or neutrophils) to kill HIV infected cells via antibody dependent cell-mediated cytolysis (ADCC). Such heteroaggregates can be assembled, for example, by covalently cross-linking the anti-HIV antibodies to the anti-CD3 antibodies using the heterobifunctional reagent N-succinimidyl-3-(2-pyridyl dithiol)propionate, as described in Karpowsky et al., J. Exp. Med. 160:1686 (1984), which is incorporated by reference herein.
Other anti-HIV agents also can be included in the formulations, such as 3xe2x80x2-azido-3xe2x80x2-deoxythymidine, 2xe2x80x2,3xe2x80x2-dideoxycytidine, 2xe2x80x2,3xe2x80x2-dideoxy-2xe2x80x2, 3xe2x80x2-didehydrocytidine, etc.
In addition to antibody compositions, compositions comprising the peptides of this invention can be administered for therapeutic and prophylactic vaccination of HIV-infected individuals. For therapeutic application, compositions comprising peptides, either as isolated peptides optionally modified as discussed above or contained within HIV proteins treated as described above and desirably coupled to an MDP microparticle to further stimulate immunogenicity, are administered to a patient infected with HIV. The amount of peptide administered is chosen so as to stimulate antibody production to functional HIV epitopes not previously recognized by the patient""s immune system so that the stimulated antibodies can arrest the infection. In prophylactic applications, compositions of the peptides coupled to the microparticle MDP are administered to persons not infected with HIV to stimulate the production of antibodies against otherwise unrecognized epitopes to provide a protective function against future infection.
Diagnostic and Prognostic Uses of Antibodies and Antigen
The antibodies and epitopes recognized by them and disclosed in the present invention also are useful for the diagnosis and management of HIV infection. Typically, diagnostic assays employing antibodies and/or their respective antigens entail the detection of the antigen-antibody complex. Numerous immunoassay configurations have been described and employ either labeled or unlabeled immunochemicals for this purpose. When unlabeled, the antibodies find use, for example, in agglutination assays, antibody dependent complement mediated cytolysis assays, and neutralization assays. Unlabeled antibodies can be used in combination with other, labeled, antibodies (second antibodies) that are reactive with the primary antibody, such as antibodies specific for immunoglobulin. Unlabeled antibodies can be used in combination with a labeled antibody which is reactive with a non-competitive epitope on the same antigen, such as in sandwich type immunoassays, or in combination with a labeled antigen. Alternatively, the antibodies can be directly labeled and used in both competitive and non-competitive immunoassays. These assay types and configurations are well known in the art. A wide variety of labels can be employed, such as radioisotopes, fluorescent tags, enzymes, enzyme substrates, enzyme cofactors, enzyme inhibitors, ligands (particularly haptens), etc. Numerous types of immunoassays are available and, by way of example, include those described in U.S. Pat. Nos. 3,817,827; 3,850,752; 3,901,654; 3,935,074; 3,984,533; 3,996,345; 4,034,074; and 4,098,876.
Commonly, the antibodies and peptides of the present invention are utilized in enzyme immunoassays, where, for example, the subject antibodies, or their respective antigens are conjugated to an enzyme and the immunoassay is configured to provide maximal sensitivity and specificity in detecting HIV antigens in biological samples such as human blood serum, saliva, semen, vaginal secretions or viral infected cell culture suspension.
Kits also can be designed for use with the subject antibodies for use in the detection of HIV infection or the presence of HIV antigen. The kits comprise antibodies of the present invention optionally in conjunction with additional antibodies specific for other epitopes of HIV. The antibodies, which can be conjugated to a label, unconjugated or bound to a solid support such as the surface of a microtiter plate well or a polystyrene bead, are included in the kits with buffers, such as Tris, phosphate, carbonate, etc., stabilizers, biocides, inert proteins, e.g., bovine serum albumin, or the like. Generally, these materials will be present in less than about 5% wt. based on the amount of active antibody, and usually present in total amount of at least about 0.001% wt. based again on the antibody concentration. Frequently, it will be desirable to include an inert extender or excipient to dilute the active ingredients, where the excipient can be present in from about 1% to 99% wt. of the total composition. Where a second antibody capable of binding to the antibody is employed, the second antibody usually will be present in a separate vial. The second antibody typically is conjugated to a label and formulated in an analogous manner with the antibody formulations described above. The subject epitope recognized by the antibody can be provided labeled or non-labeled and can be provided as part of a larger protein (synthetic, recombinant, or native), with or without modification such as the addition of spacer arms, amino groups, or cysteine residues, which can be used to attach the peptide to a support and extend it from the surface of the support. Such modifications are employed to provide the epitope in an arrangement to optimize immunoreactivity with the antibody. Such peptides are formulated in a manner analogous to that of the epitope-containing proteins as described above.
The detection of HIV antigens, or the whole virus, in various biological samples is useful in diagnosing a current infection by HIV, evaluating response to therapy, enumerating infected cells, serotyping HIV strains (clades), identifying and quantitating virulence factors associated with primary infection, progression and complications such as peripheral neuropathy, multi focal leukoencephalopathy, and Kaposi""s sarcoma. Biological samples can include, but are not limited to, blood, serum, saliva, semen, tissue biopsy samples (brain, skin, lymph nodes, spleen, etc.), cell culture supernatants, disrupted eukaryotic and bacterial expression systems, and the like. Presence of virus, viral antigens, virulence factors, and serotyping determinants are tested for by incubating the antibody with the biological sample under conditions conducive to immune complex formation, followed by the detection of complex formation. In one embodiment, complex formation is detected through use of a second antibody capable of binding to the primary antibody and typically conjugated to a label. The second antibody is formulated in a manner analogous to that described for the primary antibody formulations described above. In another embodiment, the antibody is attached to a solid phase support which then is contacted with a biological sample. Following an incubation step, labeled antibody is added to detect the bound antigen. In another embodiment, the antibody is conjugated to a detection label and following an incubation step with a biological sample, such as cells or tissue sections, the sample is evaluated by flow cytometry or microscopy for the antigen.
Peptides of this invention can be modified by introducing amino acid substitutions into the peptide. Substitutions may be desirable to vary one or more particular amino acids to more effectively mimic the epitopes of the different retroviral strains or to enhance immunological responses or MHC interactions with the epitope resulting in greater immunogenicity of the mimicked epitope when used for immunization or vaccination. In addition, it can be desirable to make certain amino acid substitutions to enhance the chemical stability of the peptide.
More specifically, a polypeptide employed in the subject invention need not be identical to any particular HIV polypeptide sequence, so long as it is able to provide immunological competition with proteins of at least one of the strains of HIV. Therefore, the subject polypeptides can be subject to various changes, such as insertions, deletions, and substitutions, either conservative or non-conservative, where such changes will enhance the desired activity of the peptide. Conservative substitutions are substitutions with similar amino acids within a group such as neutral, acidic, basic, and hydrophobic amino acids. Examples of substitutions within such groups would include gly, ala; val, ile, leu; asp, glu; asn, gln; ser, thr; lys, arg; phe, tyr; and nor, met. Additional amino acid substitutions, obtained by application of molecular modelling software to HLA allotyping database classification (DNA and serological), are shown:
In a preferred embodiment of the invention, amino acid modifications are made so as to substitute hydrophilic residues on the more hydrophilic end of the peptide of interest and hydrophobic residues on the more hydrophobic end of the peptide. Such substitutions result in the formation of an amphipathic helix with the desired epitope bracketed between the substitutions. Substituted amino acids in the D isomer can be employed to bracket epitopes to protect and stabilize the epitope and enhance immunogenicity of the epitope. Since D-amino acids are not cleaved by intracellular enzymes, such portion provides peptide epitopes of the desired length for interaction with MHC molecules when they are inserted at appropriate sites. This is described in detail in Example 8.5 below.
Usually, the modified sequence will not differ by more than about 20% from the sequence of at least one strain of the human immunodeficiency retrovirus except where additional amino acids are added at one or both termini for the purpose of providing an xe2x80x9carmxe2x80x9d by which the peptide of this invention conveniently can be immobilized on solid phase supports, attached to macro molecules or modified to enhance immunogenicity by altering or enhancing MHC binding and presentation. The arms can comprise a single amino acid or as many as 50 or more amino acids, and typically are 1 to 10 amino acids, in length.
Amino acids such as tyrosine, cysteine, lysine, glutamic or aspartic acid, or the like can be introduced at the C- or N-terminus of the peptide or oligopeptide to provide for a useful functionality for linking. Cysteine is particularly preferred to facilitate covalent coupling to other peptides or to form polymers by oxidation.
Additionally, the peptide or oligopeptide sequences can differ from the natural sequence by the sequence being modified by terminal-NH2 acylation (e.g., acetylation), thioglycolic acid amidation, or terminal carboxy amidation (e.g., with ammonia or methylamine), to provide stability, increased hydrophobicity for linking or binding to a support or other molecule, or for polymerization.
Thus, for example, in a preferred embodiment of the peptides disclosed herein, one or more cysteine residues or a combination of one or more cysteine residues with spacer amino acids can be added to the termini of the peptide. Glycine is a particularly preferred spacer when individual peptides are desired. When multiple peptide repeats of the peptide are desired, the peptide is synthesized off of a lysine core to form a tetravalent peptide repeat. The configuration is shown by way of example. Preferred peptides for use in oxidative polymerization are those in which at least two cysteine residues are added to the termini of a desired peptide. When two cysteine residues are present at the same end of the peptide, a preferred embodiment exists when the cysteine residues are separated by one to three spacer amino acid residues, preferably glycine. The presence of cysteine residues may allow the formation of dimers of the peptide and/or increase the hydrophobicity of the resulting peptide which facilitates immobilization of the peptide in solid phase or immobilized assay systems. Of particular interest is the use of the mercapto group of cysteines or thioglycolic acids used for acylating terminal amino groups or as the first amino acid for building multiple peptide repeats or the like for linking two of the peptides or oligopeptides or combinations thereof by a disulfide linkage or a longer linkage to form polymers that contain a number of epitopes. Such polymers have the advantage of increased immunological reaction. Where different peptides are desired for immunization, they are individually assembled and combined in a cocktail to provide the additional ability to induce antibodies that immunoreact with several antigenic determinants of different HIV isolates. To achieve the formation of antigenic polymers (synthetic multimers), compounds can be employed having bis-haloacetyl groups, nitroarylhalides, or the like, where the reagents are specific for these groups. The linking between the one or two mercapto groups of the peptides or oligopeptides can be a single bond or a linking group of at least 2 or more carbon atoms.
The subject peptide can be employed linked to a soluble macromolecular (e.g., not less than 5 kDal) carrier. Conveniently, the carrier can be a poly(amino acid), either naturally occurring or synthetic, to which antibodies are unlikely to be encountered in human serum. Examples of such carriers are poly-L-lysine, keyhole limpet hemocyanin, thyroglobulin, albumins, such as bovine serum albumin, tetanus toxoid, etc. The choice of the carrier is primarily dependent upon the ultimate use intended for the antigen and one of convenience and availability. In a preferred embodiment, the carrier comprises multiple repeats of glycopeptide a microparticle which can be synthesized or isolated from certain bacteria such as Proprionibacterium acini or the like. This microparticle is composed of muramyl dipeptide extensively crosslinked resulting in multimeric configurations.
When muramyl dipeptide is isolated from Propionibacterium acini or related organisms, strain selection is helpful, and selection is based on chemical analysis of the bacterial cell wall. The preferred embodiment is muramyl dipeptide extensively crosslinked with a dipeptide composed of L-alanine-D-isoglutamine.
From preliminary experiments, strain differences have been identified in which dipeptide composition and peptide length vary. Isolates with high concentrations of lipid A and O-acylated beta myristate are components of the cell wall. Preliminary experiments showed these differences are associated with increases in toxicity and decreases in adjuvant effect. Strain selection and the purification of the preferred embodiment is discussed by way of Example 4, below.
The MDP microparticle can be synthesized by employing procedures known in the art. It has been well established that MDP is a potent immunostimulant but has significant toxicity. Many attempts to reduce MDP toxicity have employed procedures to delay release, such as MDP incorporation into liposomes or other related compounds or modification of terminal groups. Chemical modification resulted in marked reduction in the desired adjuvant effect, and designs which change delivery rate have been difficult to control. By way of example, MDP microparticle configuration, size parameters, and antigen delivery attachment methods are provided below. Removal of lipids from the microparticle configuration facilitates rapid internalization of MDP by antigen presenting cells (APC). Antigen presenting cells are predominantly of monocytes lineage and include monocytes, macrophage, H istiocytes, Kuffer cells, Dendritic cells, Langerhans cells, etc. and participate in antigen processing and antigen presentation through MHC associated events. Factors which contribute to the development of immune responses to foreign protein can be, in part, determined by amino acid sequence and sequence susceptible to protease cleavage in the micro environment. Successful immune responses are most frequently observed to peptides which form an amphipathic helix with a hydrophobic terminus, preferably on the amino terminal end, and hydrophilic amino acids most frequently on the carboxyl terminal end. Sequence configurations that are resistant to protease degradation and form amphipathic helix arrangements are frequently strong immunogens. Residues which contain proline in the sequence are generally poorly immunogenic by preventing helix formation and glycosylation sites are less favorable and frequently inhibit responses directed at peptide epitopes. Antigen challenge which results in a successful immunological response in the host animal requires antigen processing and presentation of antigen through MHC associated events. Exogenous antigen is primarily processed by antigen presenting cells (APC) after internalization into endosomes. Following proteolysis by enzymes, such as cathepsin D, which are present and react in this acid environment, peptide fragments which satisfy the criteria described above are assembled with MHC class II and presented on the cell surface. When peptides are presented in sufficient density immune events result. The type of immune response is driven by the density of peptide per APC, micro-environment, the cytokine environment, and the lymphocyte type initially stimulated by antigen presenting cells.
By way of example, a unique MDP microparticle (0.01-0.2 micron) is used to deliver immunogen to antigen presenting cells resulting in immune responses to poorly immunogenic epitopes not observed using conventional methods as shown in Example 5 below. Quantitation of these immune responses demonstrate 10 to 100 fold increases in antibody concentration as compared to other adjuvants.
Subject peptides employed as immunogen can be linked to the carboxyl terminal amino acid moiety of muramyl dipeptide using either the amino or carboxyl terminus of the subject peptide or to the aldehyde oxidation product of the carbohydrate moiety as disclosed in the examples. There will be at least one molecule of the subject peptide per MDP microparticle, preferably 10-100 molecules of subject peptide per MDP microparticle and most preferably 100 to 1000 subject peptides per MDP microparticle. Carrier size and available linkage groups, therefore, will influence the number of subject peptides per carrier.
Macro-carrier composition affects immunogenicity by influencing preferential cell uptake, peptide half-life, and antigen presentation through MHC immunological events. One or more different subject peptides can be linked to the same macro-carrier but preferably a single subject peptide is attached either in the univalent or tetravalent configuration to the macro-carrier. When immunization with more than one subject peptide is desired, a cocktail of subject peptide macro-carrier conjugates can be prepared by mixing individual conjugates at ratios to optimize immunogenicity of each subject peptide introduced in the cocktail. In this configuration sufficient peptide is available on each macro-carrier conjugate (100-1000 peptides) to enhance antigen presentation by a single antigen presenting cell. Immunogenicity of the subject peptide will be optimized by adjusting both the number of subject peptides per macromolecular carrier, presentation configuration, such as amino versus carboxyl attachment, terminal amino acid modification, and space arm length and composition, as disclosed. In this configuration, antigen processing by the antigen presenting cell results in a high density, usually more than 100 and most frequently more than 500 peptides, presented at the cell surface of the antigen presenting cell through MHC interactions. With this configuration significantly higher concentrations of antibody are produced, following immunization, as shown in the examples below.
The manner of linking is conventional, employing such reagents as p-maleimidobenzoic acid, p-methyldithiobenzoic acid, maleic acid anhydride, succinic acid anhydride, glutaraldehyde, etc. The linkage can be made at the N-terminus, C-terminus, or at a site intermediate to the ends of the molecule. With multiple repeats of muramyl dipeptide, attachment of the subject peptide to aldehyde groups produced by the mild oxidation of sugar residues with, for example, sodium periodate following mild reduction with sodium borohydride and the like, the Schiff""s base intermediate is converted to a stable covalent linkage. The number of peptides per microparticle can be controlled by varying oxidation conditions and quantitated by employing a radioactive tracer. These methods are well known in the art. The method of attachment and attachment configuration can vary from peptide to peptide as needed to achieve the desired response.
Various assay protocols familiar to those skilled in the art can be employed for detecting the presence of either antibodies to retroviral protein epitopes or detecting retroviral proteins in complex protein mixtures. Of particular interest is a novel assay herein disclosed in which the subject peptide is covalently attached to a detection label such as horseradish peroxidase and the native HIV protein expressing epitope or epitopes is either directly or indirectly attached to a solid phase support. In this configuration an antibody which recognizes the peptide epitope will bridge the epitope on the solid phase with the epitope on the label. With this method the epitope reactivity of an antibody to HIV can be determined and quantitated by varying the peptides attached to the label. Peptide epitopes which are associated with HIV serotype, virulence factors or other HIV characteristics can be identified and measured in any sample expressing these epitopes by a one step competitive immunoassay herein disclosed and provided by way of example.
Use of Antibodies and Their Respective Epitopes In Immunoaffinity Purification Procedures
Antibodies specific for epitopes contained within HIV proteins and purified proteins containing these epitopes are of particular advantage for use in immunoaffinity purification of proteins and peptides containing these epitopes and antibodies reactive with them. Generally, the antibodies will have affinity association constants on the order of 108 to 1012 M. Such antibodies can be used to purify proteins and peptides containing the epitopes of interest. Oftentimes, genetically modified bacteria can be used to make HIV proteins, and the recombinant fusion proteins of interest can be purified from the culture medium of the recombinant expression system if the expressed protein is secreted, or from the components of the disrupted biological expression system if it is not secreted, or from complex biological mixtures of proteins of which some or one component contains the epitope mimicking an epitope on HIV. Generally, the antibodies which are capable of reacting with HIV epitopes are attached to or immobilized on a substrate or support. The solution containing the epitopes then is contacted with the immobilized antibody under conditions suitable for the formation of immune complexes between the antibody and the protein containing the epitope. Unbound material is separated from the bound immune complexes, and the bound proteins are released from the immobilized antibody and recovered in the eluate.
Similarly, proteins or peptides containing epitopes of HIV or mimicking epitopes of HIV can be attached to or immobilized on a substrate or support and used to isolate antibodies of interest from a solution. A solution containing the antibodies, such as plasma from which albumin has been removed, is passed through a column of immobilized peptides or proteins containing the desired epitopes and, following immune complex formation, non-reactive antibody is separated from the bound immune complex and the antibody is released with an elution buffer and recovered in the eluate. This is of particular value in purifying protein containing epitopes mimicking epitopes of HIV but derived from sources phylogenetically unrelated to HIV.
Typically, antibodies are crudely purified from hyperimmune sera. Ascites fluid or cell culture supernatants and proteins or peptides containing epitopes mimicking HIV epitopes will be crudely purified from biological sources such as, but not limited to, body fluids, blood, blood components, cell extracts, tissue extracts of both adult and embryonic origins, and culture supernatants, extracts of cultured cells, venoms, and recombinant fusion products prior to attachment to a support. Such procedures are well known by those skilled in the art and may include fractionation with neutral salts at high concentration. Other purification methods, such as ion exchange chromatography, gel filtration chromatography, preparative gel electrophoresis, or affinity chromatography, also can be used to increase the purity of the preparation prior to its use as an immunoabsorbant. Affinity purified antibody can be prepared when desired by reacting crudely purified antibody preparations with a support matrix to which the reactive epitope or protein containing the epitope has been attached.
Of particular interest are antibodies to HIV epitopes phylogenetically mimicked through nature. Such antibodies are useful as therapeutic agents and also are useful for studying HIV by allowing purification of HIV proteins and the mapping of HIV proteins for sequence location and function. Such antibodies can be produced by immunization with HIV proteins/peptides derived from HIV and immunoaffinity purified by reacting the resultant hyperimmune polyclonal multivalent antisera with proteins/peptides derived from non-HIV sources such as embryonic proteins, venoms, and non-HIV microbial/viral components immobilized on a support as discussed above. The resulting immunoaffinity purified antibody is epitope specific for an epitope or epitopes shared by HIV and the phylogenetically unrelated protein used for its immunopurification. These epitope specific antibodies have particular utility in the immunoaffinity purification of proteins and peptides of both HIV and non-HIV origin. Such antibodies can be used to map the location of the epitope on HIV to determine its sequence, evaluate functional importance in the life cycle of HIV, its distribution within the clades of HIV and among other retroviridae, its association with HIV virulence, and, when non-toxic to man but neutralizing a crucial function in the life cycle of HIV, used to treat HIV infection.
The support to which the antibodies or epitopes are immobilized desirably has the following general characteristics: (a) weak interactions with proteins in general to minimize non-specific binding, (b) good flow characteristics which allow the flow through of high molecular weight materials, (c) possession of chemical groups that can be activated or modified to allow chemical linkage of the antibody or epitope, (d) physical and chemical stability in the conditions used to link the antibody, and (e) stability to the conditions and constituents of the buffers required for absorption and elution of the antigen. Some supports commonly used are agarose, derivatized polystyrenes, polysaccharides, polyacrylamide beads, activated cellulose, glass and the like. Various chemical methods exist for the attachment of antibodies and antigens to substrate supports. See generally, Cuatrecasas, P., Advances In Enzymology 36:29 (1972). The antibodies and antigens of the present invention can be attached directly to the support or, alternatively, through a linker or spacer arm. General conditions required for immobilization of antibody and antigens to chromatographic supports are well known in the art. See, for example, Tijssen, P., 1985, Practice and Theory of Enzyme Immunoassay, which is incorporated herein by reference. Actual coupling procedures will depend slightly on the characteristics and type of the antibody or the antigen to be coupled. Attachment typically occurs through covalent bonds.
An immune serum, ascites fluid or culture supernatant rich in antibody or extract or lysate of HIV virus, the supernatant or extract from a cultured biological expression system, the supernatant or extract from a suspension of the disrupted cells tissue or blood component (adult and embryonic) or other complex protein mixtures such as venoms, body fluids, or culture products containing the epitope then is added to the appropriate separation matrix. The mixture is incubated under conditions and for a time sufficient for antigen-antibody attachment to occur, usually at least 30 minutes, more usually 2 to 24 hours. The immobilized immune complexes containing the specifically bound antibody or epitopes then are separated from the complex mixture and extensively washed with absorption buffer to remove non-bound contaminants. The immune complexes then can be dissociated with an elution buffer compatible with the particular support, the attached protein, and the eluate protein. The elutable protein, antigen, or antibody is recovered in the eluate. Elution buffers and techniques are well known by those skilled in the art. Peptides that contain the epitope recognized by the antibody can be used in the elution buffer to compete for the antibody binding site and elutions can be performed under mild elution conditions. The selectively absorbed protein can be eluted from the affinity absorbent by altering the pH and/or ionic strength of the buffer or with chaotropic agents. The selection of an elution buffer, its concentration and other eluting conditions are dependent on the characteristics of the antibody-antigen interaction, and once determined should not be subject to significant change.
The eluted protein may require adjustment to a physiologic pH and ionic strength if low or high pH or ionic strength buffers or chaotrophic agents are used to dissociate the immune complex. Such adjustment can be made by dialysis or gel filtration chromatography. These methods also permit the eluted protein to regain its native conformation.
The foregoing methods yield, e.g., substantially purified proteins containing epitopes of, or mimicking epitopes of, HIV and antibodies reactive with the epitopes. The purified proteins typically will be greater than 50% pure, more usually at least 75% pure, and frequently greater than 95% to 99% pure.
Other features and advantages of the present invention will become apparent from the following experimental descriptions, which describe the invention by way of example. The examples further illustrate the process of this invention but are not meant to limit the invention in any way.